Patent Grant
9327497
The present application claims priority from Japanese Patent Application No. 2013-239526 filed on Nov. 20, 2013, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a liquid discharge apparatus including a channel unit in which discharge ports through which liquid is discharged are formed.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2005-193435 describes that preparatory or alternative waveform is applied to an actuator to prevent the increase in viscosity of ink (to prevent the drying of ink), Further, Japanese Patent Application Laid-open No. 2005-193435 also describes that the reverberation of vibration caused by the preparatory waveform can be prevented by supplying a pulse after the pulse of the preparatory waveform to deviate therefrom by 0.54 times of the proper or characteristic period of a pressure chamber.
In the conventional technology, the interval between pulses is adjusted in view of the prevention of the reverberation of vibration caused by the preparatory waveform. Although the reverberation of vibration caused by the preparatory waveform can be prevented in the conventional technology, the vibration cannot be used effectively. Thus, there is fear that the increase in viscosity in the vicinity of meniscuses might not be effectively prevented.
An object of the present invention is to provide a liquid discharge apparatus in which meniscuses can be vibrated effectively.
According to an aspect of the present teaching, there is provided a liquid discharge apparatus configured to discharge liquid, including:
a channel unit including: a discharge port through which the liquid is discharged; a first channel through which the liquid flows to be supplied to the discharge port; and a second channel which has one end communicated with the first channel and the other end communicated with the discharge port;
an actuator including: a first electrode; a second electrode; and a piezoelectric layer sandwiched between the first and second electrodes, and being configured to apply pressure to the liquid in the second channel by deforming the piezoelectric layer relative to the second channel due to a difference in electric potential between the first and second electrodes; and
a signal supply unit configured to selectively supply a discharge driving signal and a non-discharge driving signal to the actuator, the discharge driving signal including a first voltage signal which drives the actuator to discharge the liquid from the discharge port, and the non-discharge driving signal including a plurality of second voltage signals each of which drives the actuator not to discharge the liquid from the discharge port,
wherein each of the first voltage signal and the second voltage signals goes through a first state, a second state, and a third state in this order and goes back to the first state, the first state being a state in which a voltage between the first and second electrodes is kept at a predetermined voltage, the second state being a state in which the voltage between the first and second electrodes monotonically decreases from the predetermined voltage, the third state being a state in which the voltage between the first and second electrodes monotonically increases to the predetermined voltage, and
the non-discharge driving signal is adjusted so that any two consecutive second voltage signals among the plurality of second signals satisfy a condition that: T0<Wb <T0+2Tf, where Wb is a length of time elapsed after the third state of the former second voltage signal is started until the second state of the latter second voltage signal is started, T0 is a proper vibration period of the second channel, and Tf is a length of time during which the voltage of the first voltage signal in the discharge driving signal is in the third state.
By adjusting the non-discharge driving signal in the range of the present teaching, it is possible to adequately prevent the liquid in the vicinity of meniscuses from drying as shown by an operation test which will be described later.
Hereinafter, an explanation will be made about a preferred embodiment of the present teaching while referring to the drawings.
At first, an explanation will he made about the overall structure of an inkjet printer 101 as an embodiment of a liquid discharge apparatus according to the present teaching while referring to
The printer 101 has a casing 101a in a rectangular parallelepiped shape. A discharge unit 31 is provided at an upper portion of a ceiling plate of the casing 101a. The internal space of the casing 101 a can he classified into spaces A, B, and C in this order from the top. A conveyance path which reaches the discharge unit 31 from a feed unit 1c is formed in the spaces A and B, and a sheet P is conveyed along black thick arrows depicted in
In the space A, four heads 1 which discharge the inks having mutually different four colors, a conveyance mechanism 8, a sheet sensor 32, a controller 100, and the like are disposed. The controller 100 controls the operation of each component or part of the printer to manage the operation of the entire printer 101.
The conveyance mechanism 8 includes a platen 5 and two guide units 9a, 9b to guide the sheet P. The two guide units 9a, 9b are disposed with the platen 5 intervening therebetween. The guide unit 9a disposed on the upstream side in a conveyance direction includes three guides 18a and three feed roller pairs 22 to 24, and the guide unit 9a connects the feed unit 1c and the platen 5. The guide unit 9a conveys the sheet P on which the image is to he formed to the platen 5. The guide unit 9b disposed on the downstream side in the conveyance direction includes three guides 18b and four feed roller pairs 25 to 28, and the guide unit 9b connects the platen 5 and the discharge unit 31. The guide unit 9b conveys the sheet P on which the image has been formed to the discharge unit 31.
The four heads 1 correspond to the four color inks of black, cyan, magenta, and yellow, respectively. Each of the heads 1 has a plurality of discharge ports 108 (see
The sheet sensor 32 is disposed on the upstream side of the feed roller pair 24 to detect the front end of the sheet P conveyed. A detection signal outputted when the front end of the sheet P is detected by the sheet sensor 32 is used for the synchronization between the driving of the head(s) 1 and the driving of the conveyance mechanism 8 at the time of the image formation onto the sheet P. Accordingly, the image is formed in accordance with a desired resolution and speed.
In the space B, the feed unit 1c is disposed. The feed unit 1c includes a feed tray 20 and a feed roller 21. The feed tray 20 is removably installed to the easing 101a. The feed tray 20 can load or accommodate a plurality of sheets P. The feed roller 21 feeds the sheet P positioned uppermost in the feed tray 20.
In the following explanation, a subsidiary or secondary scanning direction means a direction parallel to a conveyance direction D (direction indicated by the arrow D in
In the space C, cartridges 4 storing the four color inks respectively are detachably installed to the casing 101a. Each of the cartridges 4 storing one of the four color inks is connected to one of the heads 1 via an ink tube or the like. In a case that the ink of each of the heads 1 is consumed, the ink of one of the cartridges 4 is supplied to the head 1.
In the space A, a maintenance unit 40 is also provided. As depicted in
Subsequently, an explanation will be made in detail about a structure of the head 1 based on
As depicted in
As depicted in
The actuator unit 19 is a ceramics of lead zirconium titanate (PZT) which is ferroelectric. As depicted in
The head 1 further includes an electronic component such as a driver IC 151 (see
Subsequently, an explanation will be made in detail about the control of each part by the controller 100 while referring to
The sheet P fed from the feed tray 20 along the thick arrows in
The controller 100 controls the maintenance unit 40 to perform the wiping operation and the purge operation. In the wiping operation, the discharge surface 1a is wiped to regulate the meniscus of each discharge port 108. In the purge operation, the dried ink is discharged from the discharge ports 108. These operations restore or recover the discharge performance of ink in each of the discharge ports 108.
An explanation will be made in detail about the driving signal to be supplied to each actuator unit 19 by the driver IC 151. In the following description, “signal Sx” means a signal having a waveform Sx. As depicted in a signal S1 of
There are two kinds of driving signals in this embodiment, the driving signals including a discharge driving signal and a non-discharge driving signal. The discharge driving signal is a signal to discharge the ink from the discharge ports 108 by driving the actuator unit 19. This signal is used for the printing operation. The non-discharge driving signal is a signal to drive the actuator unit 19 to an extent that the ink is not discharged. This signal is used to prevent the ink from drying by vibrating the ink in the vicinity of each discharge port 108.
The waveform of the signal S1 of
Each individual electrode 135 is usually maintained at the electric potential V0 by the driver IC 151 in a print period during which no ink is discharged. The driver IC 151 supplies the signal S1 to the individual electrode 135 every time when a print period during which the ink is required to be discharged comes. As will be descried later, the non discharge driving signal may be supplied in the print period during which no ink is discharged. A waveform al of
In a case that the electric potential of the individual electrode 135 is kept at V0, the electric potential difference between the common electrode 134 and the individual electrode 135 is generated. The voltage corresponding to this electric potential difference is an exemplary predetermined voltage of the present teaching. Further, the state in which the voltage between the common electrode 134 and the individual electrode 135 is kept at this predetermined voltage is an exemplary first state in the present teaching. In this state, a portion, of the piezoelectric layer 141, sandwiched between these electrodes has the unimorph deformation, that is, the portion bends to be convex toward the pressure chamber 110.
In a case that the signal S1 is supplied to the individual electrode 135, the electric potential changes to have the waveform σ1, and thus the electric potential starts to monotonically decrease from V0. Then, the electric potential of the individual electrode 135 is allowed to be Vg temporarily. The state in which the voltage between the common electrode 134 and the individual electrode 135 monotonically decreases is an exemplary second state of the present teaching. In a case that the electric potential of the individual electrode 135 reaches Vg, the electric potential difference between the common electrode 134 and the individual electrode 135 no longer exists, and thus the unimorph deformation is released. By letting the unimorph deformation be released, the volume or capacity of the pressure chamber 110 increases, which applies negative pressure to the ink in the pressure chamber 110.
In a case that a time W0 has elapsed after a point of time at which the change of the electric potential from V0 to Vg is started, the electric potential of the individual electrode 135 starts to monotonically increase from Vg and is allowed to be V0 again. The state in which the voltage between the common electrode 134 and the individual electrode 135 increases monotonically is an exemplary third state of the present teaching. This causes again the electric potential difference between the common electrode 134 and the individual electrode 135, and thus the unimorph deformation occurs. The unimorph deformation decreases the volume of the pressure chamber 110, which applies positive pressure to the ink in the pressure chamber 110.
Here, W0 is adjusted so that a subsequent application of positive pressure is performed at a timing, at which the pressure wave caused to the ink in the pressure chamber 110 by the first application of negative pressure is propagated in an extending direction of the individual ink channel 132 and reversed and the peak of positive pressure comes to the pressure chamber 110. (i.e. one half of the one way propagation time of a pressure wave in the individual ink channel 132) Such W0 is equal to T0/2 in a case that the proper or characteristic vibration period of the individual ink channel 132 is made to be T0. Accordingly, the subsequent application of positive pressure is superposed on the peak of positive pressure which is caused by the first application of negative pressure, and thus the pressure is applied to the ink in the pressure chamber 110 efficiently. Therefore, the ink is discharged from each discharge port 108 efficiently. Further, W1 is adjusted so that the vibration, which is caused in the pressure chamber 110 due to the supply of a rectangular pulse, is less likely to affect the discharge of ink which is caused by the supply of a subsequent rectangular pulse.
As described above, the ink is discharged once every time when one pulse having the width W0 in the signal S1 (see
The signal S2 in
Similar to the discharge driving signal (S1), the non-discharge driving signal is configured by arranging the H signal and the L signal alternately. In each of the signals, a width of the L signal is constant and a time interval between the L signals is also constant. In the following description, the width of the L signal in the non-discharge driving signal is referred to as Wa and the time interval between the L signals is referred to as Wb. In a case that the non-discharge driving signal is supplied to the individual electrode 135, the electric potential of the individual electrode 135 monotonically decreases to Vg (exemplary second state) from the state in which the electric potential of the individual electrode 135 is maintained at V0 (exemplary first state), and then the electric potential monotonically increases (exemplary third state) to go back to the state in which the electric potential of the individual electrode 135 is maintained at V0. Thus, negative pressure is applied to the ink in the pressure chamber 110 when the electric potential of the individual electrode 135 monotonically decreases, and then positive pressure is applied to the ink in the pressure chamber 110 when the electric potential of the individual electrode 135 monotonically increases.
The width Wa of the L signal corresponds to a length ranging from the start point of the second state to the start point of the third state, and the width Wa of each of the L signals in the non-discharge driving signal is constant. The time interval Wb between the L signals corresponds to a length ranging from the start point of the third state of the former pulse, of any two pulses (for example, two pulses surrounded by the frame depicted by alternate long and two short dashes line in
Here, unlike W0 in the discharge driving signal, Wa is adjusted so that a subsequent application of positive pressure is performed at a timing which is deviated from the timing of the peak of positive pressure, which is caused in the pressure chamber 110 due to the first application of the negative pressure. That is, Wa is adjusted to be a length different from T0/2. Further, according to an exemplary operation, Wa is not more than one-fifth of the time elapsed after negative pressure is applied into the pressure chamber 110 until the vibration of the ink in each discharge port 108 peaks first. By adjusting Wa as described above, the non-discharge driving signal is adjusted so that no ink is discharged from each discharge port 108 even when the non-discharge driving signal is supplied to the individual electrode 135.
Specifically, each of the non-discharge driving signals of this embodiment is adjusted to satisfy two conditions of condition 1: Wa<Tr and condition 2: T0<Wb <T0+2* Tf. By adopting these conditions, the ink in the vicinity of each discharge port 108 (meniscus) is successfully prevented from drying as described in an operation test as will be described later. Further, each of the non-discharge driving signals is adjusted to satisfy a condition 3 in which a maximum number of pulses each having the width Wa is included, with the time interval Wb intervening therebetween, in each of the signals having a length of one print period. By meeting the condition 3, the pulses having the same width Wa are arranged, with the same time interval Wb intervening therebetween, in each of the signals. Thus, it is possible to efficiently vibrate the ink in the vicinity of each discharge port 108. Further, since the maximum number of pulses is included in each of the signals, it is possible to effectively vibrate the ink in the vicinity of each discharge port 108. Each of the signals S2 and S3 is an exemplary signal satisfying the conditions 1 to 3.
The signal S2 is adjusted to satisfy, in addition to the conditions 1 to 3, further three conditions as follows: condition 4: Wa=Tr, condition 5: Wb=T0+Tf, and condition 6: (Wa+Wb) * 4=one print period. The conditions 4 and 5 are examples of those satisfying the conditions 1 and 2. By meeting the condition 4, the electric potential of the individual electrode 135 changes as follows. That is, the electric potential decreases from VO to Vg every time when one pulse is supplied. Once the electric potential reaches Vg, the electric potential starts to increase, and then goes back to V0. By meeting the condition 5, Wb takes an intermediate value within a range of the condition 2, and thus the effect for preventing the ink from drying can be securely obtained By meeting the condition 6, in a case that the plurality of signals S2 are consecutively supplied to the individual electrode 135 without interruption, respective pulses are repeatedly supplied to the individual electrode 135 at regular intervals. Accordingly, the ink in the vicinity of each discharge port 108 can be vibrated efficiently by using the plurality of signals.
The signal S3 is adjusted to further satisfy a condition 7: Wa<Tr, in addition to the conditions 1 to 3. By meeting the condition 7, the electric potential of the individual electrode 135 changes as follows. That is, the electric potential decreases from V0 to Vg every time when one pulse is supplied. The electric potential starts to increase immediately before reaching Vg, and then goes back to V0. As described above, since the electric potential of the individual electrode 135 changes to increase before reaching Vg, the degree of unimorph deformation is also small. The intensity of pressure to be applied into the pressure chamber 110 is restricted and the magnitude of vibration caused in the meniscus in the vicinity of each discharge port 108 is restrained, and thus it is possible to prevent the ink from being discharged more reliably.
In the following, an explanation will be made about an operation test according to this embodiment while referring to
Subsequently, each head 1 is left in a state of discharging no ink for a certain period of time (for example, 10 seconds) (step A3). This promotes the drying of ink in the vicinity of each discharge port 108. Next, a predetermined number of non-discharge driving signals are supplied to the individual electrode 135 corresponding to each discharge port 108 (step A4). This vibrates the ink in the vicinity of each discharge port 108 to an extent that no ink is discharged to prevent the drying of ink. Next, the sheet P is conveyed to create a space having a predetermined distance (A in
The above operation test was performed on the heads 1 corresponding to black ink and cyan ink respectively, in a state that Wa in the non-discharge driving signal of step A4 is fixed to 1 μm and that Wb is varied between 7.0 μm and 13.0 μm by 1.0 μm. In the respective heads 1 used in this operation test, T0 was 10.0 microseconds (μs) and Tr was 1.0 μs. In this case, Tr<T0/5 is satisfied.
In the above description, the preferred embodiment of present teaching has been explained. However, the present teaching is not restricted to the above embodiment, and it is possible to make various design changes within the scope of the claims.
In the above embodiment, the signal S2 which is an exemplary non-discharge driving signal satisfies the condition 6 ((Wa+Wb)*4=one print period). Accordingly, the ink in the vicinity of each discharge port 108 can be effectively vibrated when the plurality of signals S2 are supplied to the individual electrode 135. Instead of the condition 6, it is allowable to adopt a condition: (Wa+Wb)n=one print period (n is any natural number except 4). By meeting this condition, similar to the condition 6, respective pulses are repeatedly supplied to the individual electrode 135 at regular intervals when the plurality of signals S2 are consecutively supplied to the individual electrode 135 without interruption.
The liquid discharge apparatus according to the present teaching is not limited to the printer, and the present teaching is applicable to a facsimile machine, a copying machine, and the like. The number of heads used in the liquid discharge apparatus is not limited to one. Two or more of heads may be used in the liquid discharge apparatus. The head is not limited to the head of the line type, and the head of a serial type may be used. The liquid discharge apparatus according to the present teaching may discharge liquid other than ink.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-239526 | Nov 2013 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 7416269 | Iwao | Aug 2008 | B2 |
| 20070139487 | Sekiguchi | Jun 2007 | A1 |
| 20080084457 | Hibi et al. | Apr 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 2005-193435 | Jul 2005 | JP |
| 2007-160819 | Jun 2007 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20150138265 A1 | May 2015 | US |
